1. Field
The present invention is concerned with variable capacity compressors, vacuum or other pumps or machines, and particularly those reciprocating piston compressors used in single or multiple cylinder refrigeration, air conditioning systems or heat pumps or the like, including machines such as scotch yoke compressors of U.S. Pat. No. 4,838,769, wherein it is desirable to vary the compressor output, i.e., compressor capacity modulation, in accordance with cooling load requirements. Such modulation allows large gains in efficiency while normally providing reduced sound, improved reliability, and improved creature comforts including one or more of reduced air noise, better de-humidification, warmer air in heat pump mode, or the like.
One approach to achieving modulation has been to switch the stroke length, i.e., stroke, of one or more of the reciprocating pistons whereby the volumetric capacity of the cylinder is changed. In these compressors the reciprocating motion of the piston is effected by the orbiting of a crankpin, i.e., crankshaft eccentric, which is attached to the piston by a connecting rod means of any of a variety of structures or configurations and which has a bearing in which the eccentric is rotatably mounted.
2. Prior Art
A proposed mechanism in the published art for switching stroke is the use of a cam bushing mounted on the crankshaft eccentric, which bushing when rotated on the eccentric will shift the orbit axis of the connecting rod bearing radially and parallelly with respect to the crankshaft rotational axis and thus reduce or enlarge the rod bearing orbit radius which changes the piston stroke accordingly.
A difficult problem attends such cam action mechanism in that at reduced stroke the piston does not attain full or primary stroke top-dead-center (TDC) positioning within the cylinder and greatly diminished compression and considerable reexpansion of the only partially compressed refrigerant gas occurs. The efficiency of the compressor is thus markedly compromised.
Such cam mechanisms are shown and described in U.S. patents: U.S. Pat. Nos. 4,479,419; 4,236,874; 4,494,447; 4,245,966; and 4,248,053, the disclosures of which with respect to general compressor construction and also with respect to particular structures of cylinder, piston, crankshaft, crankpin and throw shifting mechanisms are hereby incorporated herein by reference in their entirety. With respect to these patents the crankpin journal is comprised of an inner and one or more outer eccentrically configured journals, the inner journal being the outer face of the crankpin or eccentric, and the outer journal(s) being termed "eccentric cams or rings" in these patents, and being rotatably mounted or stacked on the inner journal. The bearing of the connecting rod is rotatably mounted on the outer face of the outermost journal.
In these patents, as in the present invention, all journal and bearing surfaces of the coupling structure or power transmission train of the shiftable throw piston, from the crankshaft to the connecting rod are conventionally circular.